A Metropolitan Area Network (MAN) is a communications facility allowing a number of devices to communicate with each other and generally includes workstations, interface components, connecting cables and/or fiber optics, and software for controlling the access and flow of information over the network. The MAN extends, as the name suggests, over a geographical area of a large city and uses, for example, switched Ethernet, ATM or POS as the communication protocol. The typical data rates used by MAN have increased lately from 100 Mbps to 1 Gbps and even to 10 Gbps, and new transmission protocols are under construction as specified within, for example, the IEEE 802.3 standard.
Ethernet started as a connectionless local area network (LAN) technology designed for data applications in which all stations on the network share the communication medium. The medium is shared in a peer-to-peer fashion and all devices can be reached by a single data transmission using an Ethernet frame. The protocol data unit for Ethernet is a variable length frame with a 48-bit media access control (MAC) address.
Common carrier communication links typically include relatively low speed twisted pair communication links like T1 in North America, providing a maximum data rate of 1.544 Mps, or E1 available in Europe at 2.048 Mps. High speed optical based communication links like T3 provide a maximum data rate of 45 Mps, while E3 provides 34 Mps. Networks requiring an intermediate level bandwidth, e.g. 10 to 20 Mps, must use the high speed T3/E3 carrier. This unnecessarily increases the cost of communication as the subscription rate for T3/E3 is much higher than for T1/E1, the subscriber being compelled to pay for unused bandwidth. In addition, high-speed T3/E3 links are not widely available.
It has become evident that the shared bus architecture is insufficient to meet the demands of applications that require large bandwidth, and that MANs are beginning to become a bottleneck for the modern telecommunication networks. Thus, switched Ethernet technology was developed to provide more capacity to the end-user. Rather than relying on a shared medium, this technology provides point-to-point bandwidth between the user station and the switch, so that instead of sharing, for example a 100 Mbps connection, the user gets a dedicated 100 Mbps connection.
The carrier sense multiple access with collision detection (CSMA/CD) standard defines data encapsulation/decapsulation, and media access management functions performed by the MAC sublayer. A link aggregation protocol/s (LAP), such as the LAP proposed by IEEE 802.3ad, allows one or more links to be aggregated together to form a link aggregation group, such that a MAC Client can treat the group as if it were a single link. To this end, it specifies the establishment of terminal-to-terminal logical links, consisting of parallel instances of point-to-point physical links operating at the same data rate. See “CSMA/CD Access Method and Physical Layer Specifications, IEEE Std 802.3ad-2000, Aggregation of Multiple Link Segments”, March, 2000, the content of which is incorporated herein by reference.
This point-to-point architecture has some disadvantages when the end users are located far apart. Namely, in most such cases a new physical connection needs to be established, since it is not normally easy to provision this connection over an arbitrary MAN mesh. As a result, two IEEE 802.3ad devices are generally directly connected by physical point-to-point links. This also holds true in the case of a fault in the network, where it is not easy to route the point-to-point traffic on an alternative route.
Accordingly, there is a need to provide a more flexible way of connecting two end users across a MAN.
Inverse Multiplexing for ATM (IMA) is a method for providing modular bandwidth for users accessing an ATM network, as well as for connecting ATM network elements at rates between the T1/E1 and T3/E3 levels. Asynchronous transfer mode (ATM) is a high-speed connection oriented cell-switched communications technology. Amongst other information, the ATM header contains a virtual path identifier (VPI) and a virtual channel identifier (VCI), which together form a Virtual Circuit. All the cells of a Virtual Circuit ( i.e. cells having the same VPI and VCI) follow the same path through the network. This path is determined during the call set-up procedures or by assignment.
IMA combines several physical links to collectively make up an IMA group arranged as an IMA virtual path between two specified devices. See for example the ATM Forum, “Inverse Multiplexing for ATM (IMA) Specification”, Version 1.1, March, 1999, the contents of which are incorporated herein by reference. The ATM inverse multiplexing (IMA) provides an effective method for combining multiple T1/E1 links selected to collectively provide higher intermediate rates on logical links.
Again, the IMA group is comprised of dedicated logical links connecting two specified devices. However, this protocol is specifically designed for ATM cells and can not be applied as such to Ethernet frames.
Accordingly, there is a need to provide multiple, controllable connections over the network between any two devices capable of implementing link aggregation protocols (LAP), by provisioning, without dedicating, logical links over the MAN.